KVM: X86: Restart the guest when insn_len is zero and SEV is enabled
On AMD platforms, under certain conditions insn_len may be zero on #NPF.
This can happen if a guest gets a page-fault on data access but the HW
table walker is not able to read the instruction page (e.g instruction
page is not present in memory).
Typically, when insn_len is zero, x86_emulate_instruction() walks the
guest page table and fetches the instruction bytes from guest memory.
When SEV is enabled, the guest memory is encrypted with guest-specific
key hence hypervisor will not able to fetch the instruction bytes.
In those cases we simply restart the guest.
I have encountered this issue when running kernbench inside the guest.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index e5e66e5..d5e5dbd 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4950,6 +4950,16 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
if (mmio_info_in_cache(vcpu, cr2, direct))
emulation_type = 0;
emulate:
+ /*
+ * On AMD platforms, under certain conditions insn_len may be zero on #NPF.
+ * This can happen if a guest gets a page-fault on data access but the HW
+ * table walker is not able to read the instruction page (e.g instruction
+ * page is not present in memory). In those cases we simply restart the
+ * guest.
+ */
+ if (unlikely(insn && !insn_len))
+ return 1;
+
er = x86_emulate_instruction(vcpu, cr2, emulation_type, insn, insn_len);
switch (er) {